This invention is directed to reducing the strength of adhesion of solid particulate materials, such as, for example, coal, to metal surfaces under freezing conditions causing ice formation between the materials and metal. In particular, this invention is directed to coating metal surfaces, such as the sides and bottoms of containers for storing or transporting coal, such as hopper cars, with a mixture comprising a particular hydrocarbon liquid and fatty acid which prevents moist coal from adhering to the sides or bottoms of said containers under low temperature (i.e., freezing) conditions.
Solid particulate materials, such as coal, are known to freeze when the surfaces are wet and under freezing conditions to the metal surfaces of the containers which are used to store or transport them, such as hopper cars. It is very difficult to remove the coal from the containers under these conditions. Mechanical means must be used to free the coal. However, this is time consuming and may cause damage to the car, as for example which the sides of the car are hammered in an attempt to free the coal.
The industry has attempted to solve this problem by various techniques such as by heating the hopper cars in sheds using thermal heaters. However, besides being time consuming and expensive in the energy required to operate the heaters, the heat generated by the thermal heaters can cause damage to the hopper car by, for example, weakening or melting the pneumatic lines if the heat is not carefully controlled.
In order to avoid the disadvantages occasioned by heating the cars, the surfaces of the cars which come in contact with moist coal under freezing conditions have been coated with hydrocarbon liquids, such as fuel oils. However, this technique is not effective in reducing the strength of adhesion of the frozen coal to the metal surfaces which they are in contact with.
U.S. Pat. No. 3,794,472, issued Feb. 26, 1974, describes that coal particles are prevented from freezing together and/or to the surfaces of coal storage containers by coating either the coal particles and/or the surfaces of said storage containers with a thin film of a composition comprising a hydrocarbon liquid which has emulsified therewith from 5 to 75% by weight of an aqueous solution of a polyhydric alcohol.
The sole formulation in the patent is described as containing the following ingredients: 50 percent by weight of Fuel oil--#2 Diesel, 24 percent by weight of ethylene glycol, 24 percent by weight of water and 2 percent by weight of an emulsifier which is a 50:50 weight blend of nonylphenol reacted with 9 moles of ethyleneoxide and pentaerythritol etherified with oleic acid.
In column 3, of this patent, there is described that coal particles being dropped from a storage hopper into a standard hopper type coal car are sprayed with such a composition. Also, the patent states that prior to spraying the coal, the inside surfaces of the hopper car had been sprayed with 3 gallons of the composition. After the coal was loaded into the hopper car, the outside temperature was determined to be 20.degree. F. The patent then states that the coal in the hopper car was transported to an unloading site, allowed to stand for a day and then emptied. Lastly, the patent states that the coal was readily emptied from the hopper car without any mechanical or other means being needed to unload the car.
However, at low temperatures such an emulsion has a tendency to separate into a water and an oil phase and thus become ineffective.
Thus, there exists a need for a material which will coat the metal surfaces of a container so that the adhesion of moist coal to the metal surfaces will be minimal under water freezing conditions so that the coal can be emptied from the container without the use of mechanical means or without the use of thermal heaters.